Waste incinerators are well known devices which support and confine waste as it is burned and then transport burned waste out of the combustion area for disposal.
U.S. Pat. No. 3,646,898, issued to Bavers on Mar. 7, 1982, shows such an incinerator including a horizontally disposed rotating cage for separating irreducible materials from fly ash. A flue chamber is provided for directing the flow of combustion air and flue gases through the incinerator. The Bavers device passes fly ash through the rotating screen and withdraws it from the bottom of the apparatus by suction. The Bavers device and process has several disadvantages. For example, Bavers does not make clear what the flow of draft air is, but apparently the flow is divided, as combustion gases are taught to exit via flue 24 and ash exits through sloping chute 28 and is drawn away by an exhaust blower 76. U.S. Pat. No. 3,259,085, issued to Campbell on July 5, 1966, also discloses an incinerator having a rotatable foraminated drum defining a combustion zone. These prior incinerators have not involved integrated means for separating lighter materials (predominantly fly ash) from heavier materials which are rich in recyclable resources such as aluminum and glass, nor have they shown how the heat of combustion might be reclaimed and used.
Turning to the use of an incinerator to fire a boiler, water has been heated to form steam by direct contact with an operating incinerator, but the incinerator of such a system requires heat exchange surfaces made of sufficiently heavy stock to withstand the relatively high pressure required to keep the water in a liquid state for efficient heat conduction. The heat exchange surfaces within an incinerator must also be able to withstand high temperatures and corrosion, particularly corrosion due to hydrogen chloride generated by the combustion of trash. Previous incinerating boiler designs have thus required thick heat exchange walls made of exotic metals which resist corrosion.
Although other heat transfer media for a primary coolant loop are known in other fields, particularly in the field of generating power from atomic energy (see for example U.S. Pat. No. 3,768,554, issued to Stahl on Oct. 30, 1973) the art has not made the modifications to this technology which would be necessary to suit it to a waste incinerator.
Looking now at the problem of flue gas disposal, electrostatic precipitators and water scrubbers have been used, respectively, to remove small and large particles from flue gases before releasing them, but such a system has not previously been particularly adapted for the problems of waste incineration.
All of these difficulties have hampered efficient utilization of waste as a source of energy and recyclable materials.